diff -r 7ed7b13fc00a -r 913485776542 mercurial/revlog.py
--- a/mercurial/revlog.py	Fri Feb 12 16:13:34 2021 -0800
+++ b/mercurial/revlog.py	Thu Jan 28 15:28:57 2021 +0100
@@ -83,6 +83,7 @@
     storageutil,
     stringutil,
 )
+from .pure import parsers as pureparsers
 
 # blanked usage of all the name to prevent pyflakes constraints
 # We need these name available in the module for extensions.
@@ -364,6 +365,25 @@
         return p
 
 
+indexformatv2 = struct.Struct(pureparsers.Index2Mixin.index_format)
+indexformatv2_pack = indexformatv2.pack
+
+
+class revlogv2io(object):
+    def __init__(self):
+        self.size = indexformatv2.size
+
+    def parseindex(self, data, inline):
+        index, cache = parsers.parse_index2(data, inline, revlogv2=True)
+        return index, cache
+
+    def packentry(self, entry, node, version, rev):
+        p = indexformatv2_pack(*entry)
+        if rev == 0:
+            p = versionformat_pack(version) + p[4:]
+        return p
+
+
 NodemapRevlogIO = None
 
 if util.safehasattr(parsers, 'parse_index_devel_nodemap'):
@@ -650,6 +670,8 @@
         self._io = revlogio()
         if self.version == REVLOGV0:
             self._io = revlogoldio()
+        elif fmt == REVLOGV2:
+            self._io = revlogv2io()
         elif devel_nodemap:
             self._io = NodemapRevlogIO()
         elif use_rust_index:
@@ -2337,7 +2359,13 @@
             p1r,
             p2r,
             node,
+            0,
+            0,
         )
+
+        if self.version & 0xFFFF != REVLOGV2:
+            e = e[:8]
+
         self.index.append(e)
 
         entry = self._io.packentry(e, self.node, self.version, curr)